The invention relates to vibration monitoring and acoustic leak detection in a pipeline network.
Leaks in pipelines create vibrations that can be sensed at significant distances from the leak site. These vibrations are propagated in both directions away from the leak at a constant velocity. Sensors positioned at different locations on the pipeline will sense the vibrations at different times. The time at which each sensor senses the vibration is proportional to the distance from the sensor to the leak. Leak noise correlation is a well-known technique for measuring this time delay. For example, Lander, U.S. Pat. No. 5,974,862, which is incorporated by reference, describes a technique for pinpointing a leak using digital cross-correlation. In Lander""s system, the location of the leak is determined using remote sensing units having processors in digital radio communication with a computer base station.
Other systems for longer-term monitoring of vibration signals have been proposed. For example, Bassim, U.S. Pat. No. 4,609,994, discloses a method of long-term monitoring of pipelines. Detector-analyzer units including analog circuits are deployed at intervals along a pipeline and connected to a control unit. When an analog circuit detects large vibrations originating from a pipeline failure, the corresponding detector-analyzer unit issues an alarm to the control unit.
In another approach, Virnich, U.S. Pat. No. 5,541,575, describes a leakage monitoring system having a series of integrated monitoring units digitally connected to an evaluation unit. The system functions by comparing resistive measurements from leakage sensors to baseline values recorded at a time when it was known that no leakage was present.
In one general aspect, the invention features techniques for monitoring vibrations and detecting leaks in a pipeline network by receiving vibration signals from sensors placed on a pipeline. In particular, two or more monitors, each of which includes at least a digital communication device, a timer, a processor, and a sensor, process vibration signals recorded at programmed times.
Embodiments may include one or more of the following features. For example, the timers within each monitoring unit may be time-synchronized prior to deployment. The programmed recording times may be at night when pipeline pressure and leak sounds are high and flow and environmental noise are minimal. Received vibration signals are processed individually in each monitor to model, characterize, and trend pipe vibration patterns. Vibration signals may be received regularly or intermittently over periods of hours, days, months or years. Variations in the received signals can identify leak sounds having magnitudes far below the threshold of human hearing. Processed signals may be sent to a base station, either regularly or on demand, in a flexible manner. The timers in two or more monitors may be re-synchronized using a docking station to enable time-alignment of the received signals in any number of monitors. Time-aligned received signals may be analyzed using a correlative method, which enables the detection and localization of the source of coherent sounds, such as those created by leaks in the pipeline network.
The invention offers a number of advantages. For example, distribution of monitors throughout a pipeline network allows previously unavailable information about the network to be assessed at a central or otherwise convenient location. Each monitor contains a locally-intelligent processor, which obviates the need for continuous manual surveying of the pipeline distribution system. Current and historical processed vibration signals, optimally recorded at night, can be analyzed using graphical displays of pipe sounds, listening, correlation, and other signal processing methods.
The monitors used by the invention are light-weight, low-power, cost-effective devices which may be safely applied to the pipeline network without intervention for extended periods of time. The monitors offer a high degree of protection from shocks, weather, leaking water, and vandalism. The system is virtually maintenance-free. Monitors can communicate individually or collectively by short or long range digital radio, telephone, or direct connection to a base station.
The techniques can be used to perform short or long-term serial analysis of pipeline vibrations. Monitors can detect existing leaks, newly emerging leaks, and sudden breaks or ruptures of the pipeline. Areas of particular susceptibility to pipe failure may be monitored indefinitely, preempting potentially serious problems. The techniques also can be used to perform routine surveying of the pipeline network using short-term analysis of vibrations in a particular area of the network. After detection and localization of any leaks present, the monitoring units may be initialized and deployed in a different area of the network. Mobility and short-term analysis capabilities increase the cost-effectiveness and usefulness of the invention, particularly in more sparsely populated areas.
The techniques can reliably detect leaks significantly below the threshold of human hearing due to the sensitivity to vibrations achieved by the invention""s design and signal processing capabilities.
The techniques also can account for changes in flow and pressure profiles in gas and water distribution systems due to modifications, new construction, and changes in consumption patterns. These physical changes in pipelines lead to changes in vibration characteristics. The techniques adapt to these changing system conditions in two ways. First, because each monitor""s processing is data-adaptive, individual monitors automatically adapt to locally-changing conditions. Second, the techniques can adapt to known changes in the distribution system by reprogramming the monitors from a base station using a digital communication device.
The techniques"" data-adaptive, serial analysis of vibrations is effective with all Newtonian fluids, all pipe types, and a wide range of distribution system pressures. This effectiveness is achieved because each vibration monitor acts as its own reference to analyze contemporary vibration signals with respect to trends computed from historical processed data.
The monitors can transmit alarms at different, pre-programmed levels of urgency. This means that network maintenance personnel can be alerted to the presence of leaks on high pressure gas mains or very large water mains immediately. Problems with smaller water mains and service lines can be monitored and reported at regular intervals, and scheduled for repair as appropriate. p The techniques combine the flexibility of both short and long-term monitoring. Monitors can be deployed for hours, days, months or years and can be programmed both to record at any time, and to communicate with a base station. They are thus able to pinpoint leaks by recording vibration data at the most advantageous times, such as at night.
The techniques can adapt to the pipeline conditions by unique adaptive processing of serially recorded vibration signals. This permits detection of pre-existing leaks and of emerging leaks that develop either gradually or suddenly.
The techniques are able to detect very small abnormal vibration signals, inaudible to human hearing, which are significantly below the threshold of existing detection methods. Such abnormal small vibration signals are very important to detect. They often represent the most difficult to find leaks. These leaks are typically long-lived and are the most hazardous and the most expensive in terms of lost product from the pipe. Abnormal small vibration signals may also be the harbinger of a catastrophic pipe failure. Their successful detection is the key to preventing catastrophic pipe failures before they occur.
The techniques allow deployment for any period of time. They also promise to permit pinpointing of previously undetectable leaks, and to facilitate flexible communication with a base station.
The systems employed by the techniques are almost maintenance-free and may be produced at low cost. Modes of digital communication are flexible and readily available worldwide. The network of monitors is suitable for utilities with pipeline distribution systems of almost any size and configuration. Any number of monitors can be deployed, either temporarily or permanently, to meet the needs of small rural utilities through to major cities.
Other features and advantages will be apparent from the following description, including the drawings, and from the claims.